1. Field of the Invention
The present invention relates in general to control devices for controlling internal combustion engines, and more particularly to control devices of a type which controls intake and exhaust valves of internal combustion engines.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional control device of the above-mentioned type will be described with reference to FIGS. 8 and 9 of the accompanying drawings, which is disclosed in Japanese Utility Model First Provisional Publication No. 57-198306.
In the drawings, particularly FIG. 9, denoted by numeral 2 is a cam which is rotatably disposed about a cam shaft 1. The cam 2 functions to open an intake valve 16 against a biasing force of a valve spring 17 (see FIG. 8) with an aid of a rocker arm 15. As is seen from FIG. 9, the cam 2 is positioned in an axial direction by both a cam shaft receiving bracket 3 and a flange member 5 which is secured to the cam shaft 1 by means of a key 4.
As is seen from FIGS. 8 and 9 the cam 2 has at its one end a flange portion 7 which is formed with a generally U-shaped recess 6. The above-mentioned flange member 5 is also formed with a generally U-shaped recess 8.
As is seen from FIG. 9, between the flange member 5 and the flange portion 7, there is disposed an annular member 9. The annular member 9 has at its diametrically opposed portions respective pins 10 and 11 which are slidably engaged with the U-shaped recesses 6 and 8. The annular member 9 has a cylindrical outer surface rotatably supported by a control ring 12. As is seen from FIG. 8, the control ring 12 has at its outer peripheral portion a projection 12a which is rotatably held in a supporting bore 13 formed in a cylinder head. The control ring 12 has at a diametrically opposed portion of the projection 12a an arcuate toothed portion 12b which is meshed with a toothed ring 14a provided about a rocker shaft 14.
The control ring 12 is forced to pivot in one and the other directions about the supporting bore 13 by a drive mechanism (not shown) through the toothed ring 14a and the toothed portion 12b. That is, when the center "C" of the annular member 9 assumes the position as shown in FIG. 8, the center of the cam shaft 1 and that of the annular member 9 agree with each other Thus, under this condition, the annular member 9 rotates simultaneously together with the cam shaft 1 due to engagement between the pin 11 and the U-shaped recess 8, and the cam 2 rotates simultaneously together with the cam shaft 1 due to engagement between the pin 10 and the U-shaped recess 6.
When, in response to an operation change of the engine, the rocker shaft 14 supporting the rocket arm 15 is rotated but slightly by the drive mechanism (not shown), the control ring 12 is pivoted in a certain direction using the projection 12a as a fulcrum. With this, the center "C" of the annular member 9 becomes eccentric with respect to the center of the cam shaft 1. Accordingly, the pins 10 and 11 are slid in and along the respective U-shaped recesses 6 and 8, and the flange member 5 and the flange portion 7 are pivoted about the center of the cam shaft 1 in the eccentric direction. Thus, each time the cam shaft 1 makes one turn, the rotation phase of the annular member 9 changes relative to the cam shaft 1, and at the same time, the rotation phase of the cam 2 changes relative to the annular member 9. Accordingly, the cam 2 rotates relative to the cam shaft 1 with a phase difference double that of the annular member 9 relative to the cam shaft 1. Accordingly, the valve timing can be varied in accordance with the phase difference of the cam 2.
However, due to its inherent construction, the above-mentioned control device has drawbacks which will be described in the
As is described hereinabove, each pin 10 or 11 is secured to the annular member 9 and the pin 10 or 11 is in contact with opposed side walls 6a and 6b (or, 8a and 8b) of the U-shaped recess 6 or 8. Accordingly, when a torque tile cam shaft 1 is transmitted to the cam 2 through the pins 10 and 11 and the U-shaped recesses 6 and 8, and when, due to a pivotal movement of the annular member 9, the pins 10 and 11 slide in and along the U-shaped recesses 6 and 8, a marked concentrated load tends to appear at portions where the pins 10 and 11 contact the opposed side walls 6a, 6b, 8a and 8b of the U-shaped recesses 6 and 8, which causes an increased bearing stress at such portions. Thus, the pins 10 and 11 and the opposed side walls 6a, 6b, 8a and 8b of the U-shaped recesses 6 and 8 are easily abraded and thus after long use, undesired gaps tends to appear between the pins 10 and 11 and the recesses 6 and 8. Such gaps bring about noisy movement of the pins 10 and 11 in the U-shaped recesses 6 and 8 in response to the positive and negative torque change of the cam shaft 1. Furthermore, such gaps cause a lag in valve timing. In other words, such gaps lowers the controllability of the control device.